U.S. Pat. No. 4,019,328 to Jean Marie Gerard Koehl, shows that it is known to use cross-sectionally I or H-shape beams as the structural frame of a wall support assembly for excavations such as trenches or ditches. It is also known to use wooden planks retainingly slidingly engaged into the U-shape channels of the I-beams frame, to retain the earth wall of the excavation: see U.S. Pat. No. 841,773 to Albert Fitzgerald. This latter patent also shows adjustable, elongated jack members extending transversely through an excavation, for applying compressing forces against a wall support assembly in an excavation, to bias the latter outwardly against the earth wall to prevent caving in. Fitzgerald also shows enlarged support plates at the ends of the jack members.
However, a major disadvantage of the known wall support assemblies is that the structural elements thereof usually have to be left in place in the excavation after use: they are unretrievable. This means that the whole capital cost of the wall support assembly is added to the workers' time in the computation of the overall cost for repairs in the excavation--a wasteful inefficiency. Moreover, it requires know-how to install in a proper way the wall support assemblies, while preventing any hazard to the workers installing the wall assembly, e.g. landslide while the workers are located into the excavation.